The present invention relates to a method and an apparatus for thermally treating disk-shaped substrates, especially semiconductor wafers, in a rapid heating unit having at least one first radiation source, which is spaced from the substrate, for heating at least one substrate, whereby the substrate is heated in a heating phase and is cooled in a subsequent cooling phase.
Various methods and apparatus of this type are known in the semiconductor industry. Rapid heating units, which are also known as RTP units (Rapid Thermal Processing units) can have various constructions in order to bring semiconductor wafers to temperatures over 300° C. within very short time periods, and to subsequently again cool them.
With one known RTP unit, a semiconductor wafer is vertically moved up and down in a process chamber by a mechanical handling mechanism, whereby within the process chamber a radially symmetrical and vertically changing temperature field that is constant over time is provided. This permits a rapid heating of the wafer to the desired temperature. However, there is the problem of achieving homogeneous temperatures over the wafer over time, since with this type of apparatus no compensation possibilities are provided for temperature inhomogeneities over the wafer.
With an alternative RTP unit, the semiconductor wafers are heated by radiation sources, especially halogen lamps and/or arc lamps. One example of such an RTP unit is described in applicant's DE 199 05 524 A. With this RTP unit, semiconductor wafers are transported into a process chamber having upper and lower quartz walls, and are placed upon quartz pins within the process chamber. Heating of the substrate is effected by heating lamps, such halogen lamps, that are disposed above and below the process chamber and that are respectively arranged in upper and lower banks of lamps. By appropriate control of the lamps of the upper and lower bank of lamps, temperature inhomogeneities over the surface of the substrate can be well compensated for. Furthermore, the quartz lamps enable a high heating rate of the wafer.
However, this known unit has the problem that the wafers are placed upon substrate pins, as a result of which scratches can result in the surface of the wafer during heating and expansion of the wafer. Furthermore, localized temperature gradients occur at or in the vicinity of the support points. As a result, so-called dislocations or dislocation lines result in the crystalline structure of the semiconductor wafer, and can adversely affect the function of the wafer.
Furthermore, the known units have the problem that, although they enable a rapid heating of the wafer, no cooling is possible at the same rate. This is due to the fact that the cooling of the wafer is essentially effected only via thermal radiation emitted from the wafer. Although it would be conceivable to at least partially achieve a cooling by a gas stream within the process chamber, this has the inherent problem that the gas stream can produce temperature inhomogeneities over the surface of the substrate.
It is therefore an object of the present invention to enable a rapid cooling of substrates in a rapid heating unit. Furthermore, it is also an object of the present invention to eliminate the problems resulting from support elements.